The present invention relates to a toner production system (apparatus and process) for producing a toner comprising a binder resin and a colorant for use in an image forming method, such as electrophotography.
In an image forming method, such as electrophotography, electrostatic recording or electrostatic printing, a toner is used for developing electrostatic images.
In a typical type of toner production process, toner ingredients including a binder resin for fixation onto a transfer(-receiving) material, a various colorant for providing a toner hue, a charge control agent for imparting a chargeability to toner particles, and optionally a magnetic material for imparting a conveyability to toner particles for providing a magnetic toner used in a so-called monocomponent developing method (as disclosed in JP-A 54-42141 and JP-A 55-18656) and other optional additives, such as a release agent and a flowability imparting agent, are dry-blended and melt-kneaded by a kneading apparatus, such as a roll mill or an extruder. The melt-kneaded product is, after being cooled for solidification, pulverized by means of a various pulverization apparatus, such as a jet gas stream pulverizer or a mechanical impingement pulverizer, and then classified by a various pneumatic classifier to provide toner particles having a desired particle size distribution. The toner particles are further dry-blended, as desired, with external additives, such as a flowability-improving agent and a lubricating agent, to provide a toner used for image formation. In the case of providing a two-component developer, such a toner may be blended with a various carrier, such as magnetic carrier particles, to be used for image formation.
As the pulverization means, various pulverization apparatus are used, and among these, a jet gas stream pulverizer, particularly an impingement-type pneumatic pulverizer as shown in FIG. 10, has been frequently used for pulverizing a coarsely crushed toner product comprising principally a binder resin.
In such an impingement pneumatic pulverizer using a high-pressure gas stream, such as a jet gas stream, the powdery feed (coarsely crushed product) is ejected out of an acceleration pipe to be impinged onto a surface of an impingement member disposed opposite to the accelerating pipe outlet aperture to pulverize the powdery feed under the impacting force.
For example, in the impingement-type pneumatic pulverizer shown in FIG. 10, an impingement member 164 is disposed opposite to an outlet port 163 of an acceleration pipe 162 connected to a high-pressure gas feed nozzle 161, a powdery material is sucked through a powder material feed port 165 formed intermediate the acceleration tube 162 into the acceleration tube 162 under the action of a high-pressure gas supplied to the acceleration pipe, and the powder material is ejected from the outlet port 163 together with the high-pressure gas to impinge onto the impinging surface 166 of the impingement member 164 to be pulverized under the impact. The pulverized product is discharged out of a discharge port 167.
However, as the powdery material is pulverized by the impacting force caused by the impingement of the powder ejected together with a high-pressure gas onto the impingement member, in order to produce a small particle size toner by using the above-mentioned impingement-type pneumatic pulverizer, a large amount of air is required, thus increasing the electric power consumption which results in an increase in production energy cost. In recent years, economization of toner production energy is also required from an ecological viewpoint.
Accordingly, instead of such a conventional impingement-type pneumatic pulverizer, a mechanical pulverizer not requiring a large amount of air but requiring less electric power consumption has been noted recently.
For example, a mechanical pulverizer shown in FIG. 1 has an organization including at least a rotor affixed to a central rotation shaft, and a stator disposed so as to surround the rotor with a certain spacing from the rotor, so as to provide an air-tight annular space therebetween.
Such a mechanical pulverizer does not require a large amount of air and consumes less power unlike the conventional impingement-type pneumatic pulverizer, so that it can comply with the requirement of energy economization in recent years. Further, the toner particles produced through the pulverization by such a mechanical pulverizer are provided with a rather round shape due to application of mechanical impact during the pulverization, so that the resultant toner is suitable for use in a cleanerless image forming system allowing the suppression of waste toner discharge which is desirable from the viewpoint of anti-pollution.
However, for complying with recent demands for higher quality and higher resolution images required of copying machines and printers, still severer requirements are posed on performance of the toner as a developer. For example, the toner is required to have a smaller particle size and a narrower particle size distribution free from inclusion of coarse particles and containing little ultrafine powder fraction. Further, the toner is required to have a highly controlled surface state of high level of environmental stability. More specifically, there is earnestly desired a system for efficiently providing a small particle size-toner of a sharp particle size distribution suitable for realizing high-resolution and high-definition image formation in an image forming method, such as electrophotography.
A generic object of the present invention is to provide a system, particularly a process, for efficiently producing a toner capable of providing high-definition and high-quality images.
A more specific object of the present invention is to provide a process capable of providing a toner having a small particle size and a narrow particle size distribution by using a mechanical pulverizer exhibiting a further improved pulverization efficiency.
A further object of the present invention is to provide a process for producing a toner at an excellent efficiency by using a mechanical pulverizer causing a less pressure loss at concave parts of the rotor and/or the stator thereof to exhibit an improved pulverization efficiency.
According to the present invention, there is provided a process for producing a toner, comprising: melt-kneading a mixture comprising at least a binder resin and a colorant to form a kneaded product, cooling the kneaded product, coarsely crushing the cooled kneaded product to provide a crushed product, and pulverizing the crushed product by means of a mechanical pulverizer to provide a toner having a weight-average particle size of 3 to 12 xcexcm, wherein
the mechanical pulverizer includes an inlet port for introducing the crushed product into a pulverization zone to form a pulverizate, a discharge port for discharging the pulverizate out of the pulverization zone, a rotor rotatably supported about a rotation axis and having an outer wall, a stator surrounding the rotor and having an inner wall spaced apart from the outer wall of the rotor so as to form the pulverization zone between the inner wall of the stator and the outer wall of the rotor where the crushed product is pulverized into the pulverizate,
each of the outer wall of the rotor and the inner wall of the stator is provided with a plurality of grooves which extend generally in parallel with the rotation axis of the rotor and are formed of a wave-shaped plurality of projections and intervening recesses, so that the recesses of at least one of the outer wall of the rotor and the inner wall of the stator have flat-faced bottoms, and
in case where the outer wall of the rotor has the recesses having flat-faced bottoms, each recess of the outer wall has a corner (A) at a rear edge of the flat-faced bottom with respect to the rotation direction of the rotor and adjacent to a rising slope which forms an angle (xcex11) of at least 10 deg. and below 80 deg. in a direction opposite to the rotation direction with respect to a reference line connecting the rotation axis and the corner (A), and
in case where the inner wall of the stator has the recesses having flat-faced bottoms, each recess of the inner wall has a corner (Axe2x80x2) at a forward edge of the flat-faced bottom with respect to the rotation direction of the rotor and adjacent to a rising slope which forms an angle (xcex21) of at least 10 deg. and below 80 deg. in the rotation direction with respect to a reference line connecting the rotation axis of the rotor and the corner (Axe2x80x2).
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.